The following is a list of acronyms used in the body of the specification and their definitions, which shall apply throughout the specification unless otherwise noted.
Acronyms
3GPP: 3rd Generation Partnership Project
ADS: Access Domain Selection
AS: Application Server
CAMEL: Customized Application for Mobile network Enhanced Logic
CDR: Call Data Record
CS: Circuit Switch
CSCF: Call Session Control Function
CSI: Combination of CS and IMS service
IA: IMS Adapter
ICCF: IMS Circuit Switch Control Function
ICCP: IMS Circuit Switch Control Protocol
ICS: IMS Centralized Services
IMPI: IP Multimedia Private Identity
IMS: IP Multimedia Subsystem
IMSI: International Mobile Subscriber Identity
IP-CAN: IP Connectivity Access Network
ISC: IP multimedia Subsystem Control
ISUP: ISDN User Part
MAP: Mobile Application Part
MGCF: Media Gateway Control Function
PS: Packet Switched
P-CSCF Proxy Call Session Control Function
S-CSCF Serving Call Session Control Function
SIP Session Initiation Protocol
TAS: Telephony Application Server
UE: User Equipment
URL: Uniform Resource Locator
USSD: Unstructured Supplementary Service Data
VCC: Voice Call Continuity
WCDMA: Wideband Code Division Multiple Access
FIG. 1 depicts a high-level block diagram of ICS architecture 100. IMS Centralized Services (ICS) is a proposed work item in Third Generation Partnership Project (3GPP) to make possible IMS services over many types of access networks, such as Circuit Switched (CS) network 102. Service implementation resides in IMS 110 and CS network 102 is used as an access to the services in IMS 110.
As compared to 3GPP Release 7, Voice Call Continuity (VCC) architecture, IMS CS Control Function (ICCF) 106 is introduced to allow signaling not supported over CS signaling (e.g., ISUP) such as IMS registration, mid-call signaling, additional information for call set-up signaling (e.g., SIP URL), to emulate an NMS terminal towards the IMS. Unstructured Supplementary Service Data (USSD) can be used to transport this additional signaling called ICCP (IMS CS Control) 104 in CS network.
In 3GPP Release 7 VCC, the VCC user is not IMS registered at CS access and Telephony Application Server (TAS) 108 has to implement additional mechanisms to provide IMS services to a user. A possible solution, in 3GPP Release 8, it is proposed to support IMS registration from UE 101 using ICCP so that TAS 108 can be informed from S-CSCF by a third party registration procedure that a user is IMS registered. The Serving CSCF is a call session control function for handling user equipment registration and routing for an IP multimedia subsystem. Another CSCF, the Proxy-CSC, is the first point of contact for user equipment and handles security, verification and policy decisions. Currently there is no procedure that informs the IMS whether a user is registered at CS access or at PS access (this is because there was previously no IMS registration for a CS access). IMS can only know that the user is registered at one or more radio accesses, where it is assumed that all accesses are packet-accesses. Packet Switched (PS) access has always been assumed in IMS.
Because of the assumption that the access is always PS access, there are situations that cannot be addressed by the IMS third party registration mechanism up to 3GPP Release 7. For instance, an operator may want to implement local policy in S-CSCF contact address selection to prefer CS access rather than PS access; or vice versa. An operator may want to differentiate charging for CS access and PS access and indicate that difference in IMS CDRs. Also, an operator may want to differentiate the TAS behavior if a user is registered at CS access or PS access (e.g. Call forwarding Video to Video mail box if a user is registered at CS access where video cannot be supported).
It would be advantageous to have a system and method for identifying whether a user is registered at CS or PS access that overcomes the disadvantages of the prior art. The present invention provides such a system and method.